Byers Diane L, Platenkamp Gerrit A J, Shaw Ruth G
Department of Ecology, Evolution, Behavior, University of Minnesota, Saint Paul, Minnesota, 55108.
Department of Botany and Plant Sciences, University of California, Riverside, California, 92521.
Evolution. 1997 Oct;51(5):1445-1456. doi: 10.1111/j.1558-5646.1997.tb01468.x.
A growing body of evidence indicates that phenotypic selection on juvenile traits of both plants and animals may be considerable. Because juvenile traits are typically subject to maternal effects and often have low heritabilities, adaptive responses to natural selection on these traits may seem unlikely. To determine the potential for evolutionary response to selection on juvenile traits of Nemophila menziesii (Hydrophyllaceae), we conducted two quantitative genetic studies. A reciprocal factorial cross, involving 16 parents and 1960 progeny, demonstrated a significant maternal component of variance in seed mass and additive genetic component of variance in germination time. This experiment also suggested that interaction between parents, though small, provides highly significant contributions to the variance of both traits. Such a parental interaction could arise by diverse mechanisms, including dependence of nuclear gene expression on cytoplasmic genotype, but the design of this experiment could not distinguish this from other possible causes, such as effects on progeny phenotype of interaction between the environmental conditions of both parents. The second experiment, spanning three generations with over 11,000 observations, was designed for investigation of the additive genetic variance in maternal effect, assessment of paternal effects, as well as further partitioning of the parental interaction identified in the reciprocal factorial experiment. It yielded no consistent evidence of paternal effects on seed mass, nor of parental interactions. Our inference of such interaction effects from the first experiment was evidently an artifact of failing to account for the substantial variance among fruits within crosses. The maternal effect was found to have a large additive genetic component, accounting for at least 20% of the variation in individual seed mass. This result suggests that there is appreciable potential for response to selection on seed mass through evolution of the maternal effect. We discuss aspects that may nevertheless limit response to individual selection on seed mass, including trade-offs between the size of individual seeds and germination time and between the number of seeds a maternal plant can mature and their mean size.
越来越多的证据表明，对植物和动物幼体性状的表型选择可能相当可观。由于幼体性状通常受到母体效应的影响，且遗传力往往较低，因此对这些性状进行自然选择的适应性反应似乎不太可能。为了确定对弯叶沟酸浆（紫草科）幼体性状选择的进化反应潜力，我们进行了两项数量遗传学研究。一个涉及16个亲本和1960个后代的正反交析因杂交实验表明，种子质量的方差存在显著的母体成分，发芽时间的方差存在加性遗传成分。该实验还表明，亲本之间的相互作用虽然很小，但对这两个性状的方差有非常显著的贡献。这种亲本相互作用可能通过多种机制产生，包括核基因表达对细胞质基因型的依赖性，但该实验的设计无法将其与其他可能的原因区分开来，例如双亲环境条件之间的相互作用对后代表型的影响。第二项实验跨越三代，有超过11000次观测，旨在研究母体效应中的加性遗传方差、评估父本效应，以及进一步划分在正反交析因实验中确定的亲本相互作用。该实验没有得出父本对种子质量有影响以及亲本相互作用的一致证据。我们从第一个实验中推断出的这种相互作用效应显然是由于没有考虑到杂交中果实之间的巨大差异而产生的假象。结果发现母体效应有很大的加性遗传成分，至少占个体种子质量变异的20%。这一结果表明，通过母体效应的进化，对种子质量选择的反应有相当大的潜力。我们讨论了可能限制对种子质量个体选择反应的各个方面，包括单个种子大小与发芽时间之间的权衡，以及母本植物能够成熟的种子数量与其平均大小之间的权衡。
